The compound 1-0-alkyl-2-acetyl-SN-glycero-3-phosphocholine (AAGPC) appears indistinguishable from naturally-occurring platelet-activating factor (PAF) and an antihypertensive lipid (APRL). This unique phospholipid mediator expresses its anaphylactic and antihypertensive properties when administered in nanomolar quantities and is rapidly deactivated in vivo, possibly by a specific acetylhydrolase. No analogues prepared to date have shown a clear separation of the two bioactivities mentioned above nor are the mechanisms of action known, although it appears that the mechanisms do not involve direct acetylation of a protein. The analogues described herein will further the structure-activity relationship (SAR) study underway and identify functional groups associated primarily with either hypertensive or anaphylactic responses. Other analogues containing spin labels or radiolabeled photoactivatable groups will define the biological environment of the PAF molecule and identify the putative receptor(s) involved by binding covalently to the receptor molecule. Elucidation of the mechanism(s) of action and the receptor(s) involved in binding PAF will lead to analogues that may prolong the duration of action of PAF (via substrates having a higher binding affinity for the putative receptors or a lower affinity for the acetylhydralase receptor) or may inhibit the acetylhydrolase enzyme and prolong the action of endogenous PAF. Identification of functional groups associated primarily with anaphylactic or antihypertensive responses may lead to analogues of PAF that would be inhibitors of the anaphylactic bioactivity and provide a new class of durgs to treat hypertension.